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Old 13-10-2021, 08:12 PM
Martin Pugh
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Location: Canberra, Australia
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Pedestal

Hi there

when and where do you think a pedestal is applied?
Is it by the manufacturers driver, the camera control program or by the program used for image calibration?

I am trying to resolve a smattering of black specs that appear in my QHY600 images after image calibration......and I understand the need for identical gain/offset/readout modes, and I understand that the offset is designed to prevent this, but no matter what value I set, I still get those black specs.

thanks
Martin
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Old 13-10-2021, 08:33 PM
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gregbradley
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The offset with a QHY600m is set in the driver. I use Sky X and there is a plug in driver for Sky X. In the setup box you set the mode, the gain and the offset.

In my limited experience I have found I got good calibration using mismatched lights and calibration files with regards to mode, gain and offset.

The settings I use for QHY600 are:

1. Mode 0 Gain 26 Offset 40 for broadband objects.

2. Mode 1 Gain 56 Offset 50 for narrowband.

These seem to work well. There is also the mode 2 high gain mode with double sampling for extended full well. I would use that in an object with a very bright star in the field along with short exposures.

I also sometimes see black specs in calibrated files but these clean up using data rejection in CCDstack removing hot and cold pixels. Mostly see these in narrowband images and also seen them with CCD cameras as well.

The differences in my opinion in exposures done with the various modes are not that different one to the next. But enough of a difference to make it worth while. The increased library of calibration files though is just another layer of complexity so that is a moderating factor.

Greg.
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Old 13-10-2021, 08:44 PM
Martin Pugh
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Thanks Greg. I am aware of this, but my question regards where the pedestal is applied.

You open an image in CCDSTACK for example, and one camera will show 0 as a pedestal, and another camera will show 100 as a pedestal. It is where/when this is applied I am trying to get to.

BTW...You should test the Ultra Full Well and Extended CMS modes...they do not work. Look at the images they produce.....light gradient from left to right and banding.

I also use High Gain mode, but do not change from one readout mode to another, dont see the point really. The 2 modes you use only have a minor difference in read noise, but obviously the full well is significantly more with Mode 1. What is your reason for changing from one to the other?

thanks
Martin
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